Long-Term Skin Regeneration From a Gene-Targeted Human Epidermal Stem Cell Clone

Ex vivo gene therapy is one of the current strategies being tested to treat genodermatoses such as epidermolysis bullosa (EB).1 In fact, Mavilio et al. proved the feasibility of this therapeutic modality in a patient with the junctional form of EB (JEB).2 Efforts are now being directed toward the development of efficient approaches minimizing potential genotoxic effects due to vector-induced insertional mutagenesis. Gene correction by gene editing through nucleasefacilitated homologous recombination (HR) has recently been proven to be achievable on recessive dystrophic EB cells that were subsequently reprogrammed to induced pluripotent stem cells (iPSCs) and differentiated to collagen VII–expressing keratinocytes.3 We have also demonstrated the feasibility of zinc-finger nuclease–facilitated, HR-mediated insertion of a marker gene into the intron 1 of the PPP1R12C gene (AAVS1 locus) in a limited number of human epidermal repopulating cells that, upon grafting, persisted as small foci in skin regenerated in immunodeficient mice.4 In this study we report that engraftment and persistent skin regeneration can be achieved with an expanded stem cell clone isolated from AAVS1 gene–targeted human keratinocytes.